While sales of computers have slid over the last few years, small companies that make custom computers have grown. The dividing line between those who care about PC performance and those who don’t is more distinct than ever. Specialists like Falcon Northwest, Origin and Digital Storm are where it’s at.

Buying a customized PC isn’t the same as buying an off-the-shelf model, however. While you don’t build the system yourself, you are responsible for picking the components, and a mistake could mean spending hundreds, even thousands, more than necessary. Here’s what you should know before you take your system through checkout.